用issue,problem和question填空
问题描述：
用issue,problem和question填空
There have been so many trade______ since China joined the WTO.
The best way is to get to the root (heart) of the_____.
Unemployment is a very serious ______for graduates now.
The key ______of what caused the leak remains unanswered.
In an interview try to ask some open _____ that don't just need "Yes" or "No" as answers.
答
issue
problem
problem
problem
questions
这里的issue不用加s吗？是要加s，没仔细看。